Steel mill optical width gage



Jan. 13, 1959 H. R. sUMMERHAYEs, JR 2,868,059

STEEL MILL OPTICAL WIDTH GAGE 3 Sheets-Sheet 1 Filed Oct. 5. 1953 lmung* Invenlov v'Iavrv-- R. Summevhages Jn,

His Abovneg.

b5 mmf/@gw INN Jan. 13, 1959 H. R. sUMMERHAYEs, JR $868,059

sTEEL MILL OPTICAL WIDTH GAGE Filed oct. 5, 1953 E sheets-sheet 2 vInventor Harrg R. SIa'rnfner'xak;esa,r Jn,

by 04mg Hts Gborneg PWER Sl/PPL Y Jan. 13, 1959 Hf R. SUMMERHAYES, JR2,868,059

sTEEL MILL OPTICAL WIDTH GAGE 3 Sheets-Sheet 5 Filed Oct. 5. 1955 hventor b: Harry R. Summerhagesn,

bw @da @/@w His bAbb ovneg United STEEL MILL OPTICAL WIDTH GAGE Harry R.Summerhayes, Jr., Schenectady, N. Y., assignor t; eneral ElectricCompany, a corporation of New Application October 5, 1953, Serial No.384,299

s Claims. (ci. :ss-14) tory for many purposes, they have not beenentirely suitable for use in certain types of installations. Inparticular, the known non-contacting width gages have not been entirelysuitable for use in mills for rolling out relatively wide strips of hotsteel having temperatures ranging between 1350 F. to 2050 F. whereincooling effects at the edge of the hot steel strip as well as scale onthe steel strip, tend to produce false indications of the width of thestrip. Further, because of the wide range of steel strip temperatureslover which the gage must operate, the operation of known gages has notbeen entirely satisfactory at higher strip temperature values due to thefact that such gages use conventional automatic volume control circuitsto effect gain control, and at the higher strip temperature values theautomatic volume control bias is so grcatthat it causes electron tubesin the circuit being controlled to be overdriven with resultantdistortion of the output signal.

It is therefore one object of the present invention to provide a noveltrigger circuit arrangement for a multivibrator, and a new and improvednon-contacting Width gage having the novel trigger circuitincludedtherein wherein effects of edge cooling do not produceundesirable triggering action With a resultant false indication ofwidth.

Still another object of the invention is to produce a novel triggercircuit arrangement for a non-contacting width gage which does notproduce a false indication in response to the eHect of scale on the hotsteel strip being gaged. y

A still further object of the invention is to provide a new and improvedphototube gain control circuit for use in non-contacting width gageswherein the phototube is subjected to a wide range of luminositiescaused by widely varying strip temperatures.

In practicing the invention, a photocell gain control 4f circuit isprovided which includes a photoelectric device, an electron dischargedevice having a plurality of control electrodes with the photoelectricdevice being coupled between two of the control electrodes of theelectron discharge device, and means for providing a varying controlelectric signal to one of the tube-control electrodes to which thephotoelectric device is coupled. Also, in practicing the invention, anovel wave shaping circuit for a bi-stable multivibrator having twostable states of operation is provided. This circuit includes aditferentiating circuit which is operatively coupled to the input of thebi-stable multivibrator, and a second conducting path tate arent O2,868,059 Patented Jan. 13, 1959 2 operatively coupled to the input ofthe bi-stable multivibrator in parallel circuit relationship with thedifferentiating circuit for bypassing at least a portion of theundifferentiated input signal supplied to the input of the multivibratorin conjunction with the differentiating signal thus applied. In theirpreferred form, the above-identilied circuit arrangements are includedin Va non-contacting width gage which comprises a pair of photoelectricdevices positioned to view respective opposite edges of an object beinggaged, together with means for scanning the view of each of thephotosensitive devices in the direction of the width of the object sothat the same are capable of producing substantially square wave shapealternating electric signals that are representative of the width of theobject in the area of view of the respective photoelectric device. Aphotoelectric device gain control circuit is also included in thearrangement and comprises an electron discharge device having aplurality of control electrodes with each of the photoelectric devicesbeing coupled between the two control electrodes of the respectiveelectron discharge devices thereof, and means operatively coupled to oneof the two control electrodes to which the photoelectric device iscoupled for providing a varying gain control electric signal thereto.Respective wave shaping circuits are coupled to the output of each ofthe electron discharge devices, and each comprises a bi-stablemultivibrator, a differentiating circuit coupled between the output ofthe electron discharge device and the respective multivibrator, and asecond conductive path coupled between the output of the electrondischarge device and the input to the multivibrator in parallel circuitrelationship with the differentiating circuit. A common outputindicating circuit is operatively coupled in common to the output ofboth of the said bi-stable multivibrators to provide an outputindication of the width of the object being gaged.

Other objects, features, and many of the attendant advantages of thisinvention will be appreciated more readily as the same becomes betterunderstood by reference to the following detail description, whenconsidered in connection with the accompanying drawings, wherein likeparts in each of the several figures are identiied by the same referencecharacter, and wherein:

Fig. 1 is a schematic block diagram of an improved steel mill width gageconstructed in accordance with the principles of the present invention;

Fig. 2 is a detailed circuit diagram of the width gage illustratedschematically in Fig. 1; and

Fig. 3 is a series of voltage versus time plots of the signal voltagesoccurring in a portion of the steel mill width gage illustrated in Figs.1 and 2.

The new and improved non-contacting width gage illusstrated in Fig. 1comprises a pair of photoelectric devices 11 and 12 which preferablycomprise gas lled photo tubes having a gas amplification factor by whichthe magnitude of the applied D. C. voltage controls the magnitude' ofthe originally emitted photoelectric current. The phototubes 11 and 12are positioned to view respective opposite edges of an object, such as asteel mill strip 13 disposed on rollers 14 through lenses 15 and 16,respectively. A means for scanning the View of each of the phototubes 1land 12 in the direction of the width of the steel strip 13 is provided,and preferably comprises a pair of rotatable mechanical scanners 17 and1S, respectively.

. For a more detailed description of the construction and operation ofthe mechanical scanners 17 and 18, reference is made to theabove-identified copending application; however, briey, the rotatablemechanical scanners coact with a slit 19 in dust-tight housings 21surrounding each of the phototubes 11 and 12, respectively, to provide alinear scanning movement over the edge of the steel'mill strip 13through an arc of travel such as is indicated by the dotted lines inFig. l of the drawings. This scanning action serves to develop asubstantially square wave electric signal in the output of thephototubes 11 and 12 which is indicative of the width of the object 13in the area of view of thev phototube. This square wave electric signalis developed due tothe fact that the steel strip 13V is` at an elevatedtemperature with respect to the background provided by rollerslfi, andpreferably is in the form of a red hot strip which emits light rays of acomparatively high amplitude in comparison to the background level ofradiation. Hence, as the view of each of the photocells is swept backand forth across the edge of thestrip 13, a substantially square waveelectric signal is produced in the output of each of the phototubes.

The output electric signals developed by each of the phototubes 11 and12 are: coupled to the input of a pair of wave shaping preamplifiers 22and 23, respectively, andl from the preampliiiers to a pair of waveshaping channels 24 and 25, respectively. The construction and operationof the wave shaping preamplifiers and channels will be described morefully hereinafter; however, for the present it is suflicient to pointout that the channels 24 and 25 serve to derive two separate squarewave, pulsed electric signals whose pulse width is indicative of thewidth of the object being gaged. These square wave output signals arefed to a common output indicating circuit which includes an addercircuit 26 coupled to the input of a filter 27 which is in turnconnected to a deviation indicator 28.

For a more detailed description of the construction and operation of thewave shaping preampliliers 22 and channel 24, reference is now made toFig. 2 of the drawings. As each of the wave shaping amplifiers 22 and23, and each of the channels 24 and 25, are similar in construction, thedescription will be limited to only one of the amplifiers 22 and itscorresponding wave shaping channel 24. The energizing potential issupplied to the phototube 11 from a resistance divider comprised of aplurality of series connected resistors 31, 32, 33, and 34 connectedacross a source of direct current potential supply B+. The collectorelectrode of the phototube 11 is connected to the potential divider31-34 through a coupling resistor 35 and smoothing capacitor 36, and isconnected through a coupling capacitor 37 to the control grid of amultielectrode electron discharge device comprising a pentode 38. Theemitter electrode of the phototube 11 is connected through a suitableconductor 39 to the screen grid of the pentode 38, and suitable biasingpotentials are supplied to the pentode from the source of direct currentpotential B+ through a plate load resistor 40, a cathode resistor 41, aresistance divider comprising resistors 42 and 43 which has a pointthereon connected to the screen grid of pentode 38 and by passes toground through a capacitor 44 audio frequency signals resulting from thescanning motion and a direct current connection between the suppressorgrid of the pentode and ground.

The plate electrode of the pentode 33 is connected through a novel waveshaping circuit that comprises a ditferentiator composed of a capacitor45 and a resistor 46 to the control grid of a two stage amplifierconsisting of the two triode sections of a duo triode tube 47. Inaddition to the differentiator circuit, a second conductive path isprovided between the plate electrode of the pentode 38 and the controlgrid of the first triode section of tube 47 in parallel with theditferentiator circuit. This conductive path preferably comprises a D.C.blocking capacitor 48 connected in series with an attenuating resistor49, the series circuit thus comprised being connected in parallel withthe differentiator circuit to the control grid of the first triodesection of tube 47.

The iirstl stage amplifier formed by the first triode section ofltube 47comprises a standard direct coupled amplitier having a cathode biasingresistor 51 and a plate load resistor 52, with the output thereofconnectedk directly to the second stage amplifier whichv comprises acathode follower amplifier having a cathode load resistor 53. The outputsignal developed across load resistor 53 is supplied through a couplingline 54 which, as is shown in Fig. 1 of the drawing, serves to couplethe preamplifier section 22 to the wave shaping channel 24. Thepreamplified electric signal supplied through the coupling conductor 54is applied through a coupling network cornprising a capacitor 55, aresistor 56, and a resistor 57 to the control grid of the iirst triodesection of a duo-triode tube 53 to which proper biasing potentials aresupplied by a potential divider formed by a resistor 59 and a cathodeload resistor 61 connected in series circuit relationship across thesource Ofdirect electric potential B+ and by a plate load resistor 62.The amplifier thus constructed serves to amplify the differentiated andrecombined signal supplied thereto through coupling line 54, and toapply the amplified signal to two different output connections.

One of the output connections from the plate load resistor 62 of the rsttriode section of tube 58 is fed through a coupling capacitor 63 to theinput of a bistable multivibrator Vcomprised of two triode sections 64and 65 of a duo-triode tube. The bi-stable multivibrator 64, 65 is ofstandard construction and has the plate of triode section 65 connectedto the control grid of the triode section 64 through a couplingcapacitor 66 and resistors 67 and 68, respectively, while the anode oftriode section 64 is connected to the control grid of triode section 65through a coupling resistor 69. The triode sections have a commoncathode load resistor 70, and separate plate load resistors 71 and 72,respectively. A suitable bias' potential is applied to the control gridof the triode section 64 from a voltage divider comprised of a pluralityof series connected resistors 73, 74, and 75 coupled to the saidcontro-l grid through a coupling resistor 76 and resistor 68 while aproper bias is supplied to the control grid of the triode section 65from a potential divider composed of the plate loadv resistor 71 oftriode section 64 the coupling resistor 69, and a resistor 77 connectedbetween the` control grid and ground. The potential applied to each ofthe control grids is such that either theV triode section 65 isconducting or the triode section 64 is conducting, depending upon whichcondition the last triggering pulse supplied to the multivibrator leavesit. Upon application of a voltagepulse to the control grid of the triodesection 64, the condition of that triode section is changed to render iteither conductive or non-conductive and the condition of triode section65 is likewise changed due to a voltage pulse applied to the controlgrid thereof through the coupling resistor 69 and to a voltage pulseapplied to the cathode through the common cathode resistor 70. Thiscondition is maintained until the next succeeding voltage pulse isapplied tothe control grid of the triode section; in which event thecondition of triode section 64 is again changed to thereby return thebi-stable multivibrator to its initial condition to complete a cycle ofoperation. Succeeding Voltage pulsesrepeat the cycle.

The wave shape of the sequence ofl electric signals occurring in theabove-described' portions of the width gage, is illustrated in Fig. 3 ofthe drawings wherein Fig. 3A showsl a substantially square wave electricsignal produced by the phototube 111 and ampliiiedl by pentode ampliiier38. This electric signal has a slopingl leading edge such as shown at 78due to the eiiects of edge cooling of the hot strip steel observed bythe phototube. In the previously' known arrangement set forth in theabove-identilied copending application, Serial No. 240,259, now PatentNo. 2,791,931, the mid portion of the electric signal having a waveshape such as shown infFig. 3A, wasl clipped out between the levelsindicated at 79- and 81, and this mid portion used to derive anindication-ofi the widthfof `the strip being-gaged, As is apparent fromFig. 3A, however, the edge cooling effect alters the width of the midportion of the square wave l signal, so that an erroneous reading of thewidth is obtained by this method. For this reason the system was notsufiiciently accurate to be relied upon for all types of installationsin which the gage might be used. To overcome this defect, it wassuggested that the signals shown in Fig. 3A be differentiated to producean output signal such as shown in Fig. 3B, and the differentiated waveused to trigger off a multivibrator such as 64, 65. The multivibratortriggers at certain predetermined levels, as illustrated by the lines 82and 83, so that upon the occurrence a leading voltage pip 84, whichcorresponds in time to the leading edge of the substantially square waveshaped signal shown in Fig. 3A, the multivibrator is triggered from oneof its stable states of operation 'to a second, and upon the occurrenceof the trailing voltage pip 85 of the differentiated wave, themultivibrator is y triggered back to its initial state of operation.While a system of this nature is theoretically capable of accurateoperation, under actual conditions the substantially square wave shownin Fig. 3A has certain transit impulses occurring therein due to theeffect of scale on the hot strip steel being gaged. Upon differentiatingof the square wave-shape signal then, relatively large amplitude pipwaveform Voltage peaks are obtained which, in the instance shown in Fig.3B, might be sufficiently large -to falsely trigger the multivibrator64, 65, and hence result in the production'of an erroneous indication ofwidth. In order to overcome this last mentioned difficulty, the waveshaping circuit comprising a part of the present invention wasdeveloped. This wave shaping circuit comprises the differcntiatorcircuit formed by capacitor 45 and resistor 46, and the D.C. blockingcapacitor 48 and attenuating resistor 49 connected in parallel circuitrelationship therewith in the input of two stage amplifier 47. By reasonof this connection, a certain portion of the undifferentiated inputsignal shown in Fig. 3A is coupled through the attenuating resistor 49and D.C. blocking capacitor48 to the control grid of the first stage ofamplifier 47 along with the differentiated signal supplied throughdiferentiator circuit 45 and 46. In this manner, the reference level ofthe `differentiated voltage peaks occurring because of scale are raisedto a point that the negative going portion of such voltage peaks doesnot extend to the trigger level of the multivibrator, and hence cannotfalsely trigger the multivibrator. The resulting waveform is shown inFig. 3C of the drawings. In Fig. 3C it can be seen that the'l'eadingpositive going voltage peak 84 will trigger the multivibrator from oneof its stable states of operation to the otherv and subsequent undesiredpositive going voltage peaks due to scale will not affect it due to theinherent nature of the multivibrator. The negative going portions ofsuch transient voltage peaks have been lifted by the portion of thesignal reinserted by capacitor 48 and resistor 49, that is, the absoluteamplitude of the negative go-ing peaks have been raised 'to a point suchthat they do not extend to a sufficiently low value to trigger themultivibrator back to its initial state of operation, and only thenegative going voltage peaks 85 occurring at the trailing edge of thesubstantially square wave signal shown in 3A extends to a lsufficientlylow value to produce such a triggering action. t

From the foregoing description, it can be appreciated that thephotoelectric device in each of the scanning channels serves to developasubstantially square waveshape signal such as that shown in Fig. 3A.This signal is amplified 4by amplifier 38, and supplied to the waveshaping circuit comprising differentiator 45, 46 and attenuatingresistor 49 connected in parallel to the input of amplifier 47. `Thewave shaping circuit serves to differentiate the signal shown at Fig.3A, and to reinsert a portion of the undifferentiated signal back intothe differentiated signal to serve as a base or floor thereby resultingin the composite waveform signal shown in Fig. 3C. This cornpositewaveform signal is amplified by amplifier 47, supplied through couplingconductor 54, and further amplified by amplifier 58 before being appliedto the input of multivibrator 64, 65 to control the operation thereof.The resulting square wave signal produced at the output of themultivibrator is shown in Fig. 3D of the drawings and provides areliable indication of the width of the substantially square wave inputpulse developed by photoelectric device 11, and hence the width of theportion or side of the steel strip being viewed. A similar signal isavailable at the output of channel which is identical in constructionand operation to the above-described channel. Hence by properlycombining the two square wave signals produced by the multivibrators ineach channel, an output indication of the total width of the strip beinggaged can be obtained.

The square wave output signal produced by the multivibrators in each ofthe channels 24 and 25 are supplied through coupling resistors 86 and 87respectively to a common output indicating circuit which includes atotalling resistor 88. Totalling resistor 88 is in turn connectedthrough an integrating or smoothing filter 89 that includes a pluralityof resistors 91, 92, 93 connected in a dual T network arrangement with aplurality of -capacitors 94, 95, 96. The filter network 89 is connectedto the control grid of one triode section of a two triode differentialamplifier 97 having the control grid of the remaining triode sectionthereof connected to a source of reference potential comprising aresistance voltage divider 98 connected between the source of D.C.positive potential B+ and ground. Separate load resistors 99 and 101 areconnected in the cathode circuits of each of the triode sections of thedifferential amplifier 97, and a suitable indicating instrument of themoving coil galvanometer type 102 is interconnected between the cathodeload resistors along with adjustable Calibrating resistors 103 and 104.

By this construction, the combined square wave output of each of themultivibrators 64, 65 in both channels 24 and 25 is applied through thetotalizing resistor S8 and through the integrating filter network 89 tothe control grid of one of the triode sections of the differentialamplifier 97 and compared in magnitude to the reference potentialobtained in the voltage divider 98. If this reference potential isinitially set to indicate a predetermined width and the steel stripvbeing gaged is on gage, each of the triode sections will conduct anequal amount of current, no difference in potential will exist acrossthe load resistors 99 and 101, and hence no indication of deviation Willbe derived from indicating meter 102. However, should the width of thestrip being gaged deviate from desired value, the amount of conductionoccurring in the first triode section of tube 97 to which the output ofthe multivibrators is applied, will be either less or more than theconduction occurring in the second triode section, thereby producing adifference of potential across the cathode load resistors 99, 101 whichwill appear as an indication on the indicating meter 102. The amount ofdeviation of the indicating meter 102 will be an indication of thedeviation of the width of the strip from a desired standard.

In order that the width gage be satisfactory for use in gaging stripshaving widely varying temperature values, and, hence, widely varyingluminosities, a connection is provided from the plate electrode of theamplifier 58 through a differentiating circuit comprising a capacitor105 and resistor 106 to the control grid of an amplifier 107 having acathode biasing resistor108and a plate load resistor 109. The amplifier107 serves to amplify the doubly differentiated output signal from theamplifier 58, and this amplified, differentiated signal is fed through aresistance-capacitance coupling circuit comprising a ca- 7 pacitor 111and a resistor 112 to a diode detector 11 having a' smoothing filtercircuit connected in its output. The filter circuit is formed by aresistor 114 and a capacitor 1715 connected in parallel circuitrelationship, and has a relatively slow time constant. The output of theilter circuit is connected through a conductor 116 and a suitableresistance-capacitance coupling network to further filter out thescanning signal frequencies comprising resistors 117, 118, and 119 andcapacitor 120, back to the control grid of the pentode amplier 38 in thepreamplitf her circuit arrangement.

The operation of the automatic gain control circuit thus constructed,and its advantages over previous circuits of the same nature, will bemore apparent after a reading of the following. discussion: In'conventional amplier automatic gain control circuits, the gain of theamplier is controlled automatically by a feedback system which comparesthe transient signal amplitude of the amplifier with a standardamplitude, and utilizes the difference as a gain controlling factor tovary a grid bias voltage of an electron discharge tube included in thecircuit being controlled. In the case of width gages, however, where therange of the input signals is very large, about to l or more, this kindof control was found to be inadequate due to the fact that the maximuminput signal level required such a large automatic gain control bias toproduce a proper output that the input amplier was cut off during aportion of the alternations occurring in the input signal. Thus,undesired distortion of the input signal would occur. In order toeliminate this source of distortion, and yet retain control over thegain of the circuit, the above-described double acting automatic gaincontrol system was devised wherein, in addition to the usual automaticgrid bias control provided by conventionalautomatic gain controlcircuits, the above-described circuit provides an additional control dueto the fact that the emitter electrode of the phototube 11 is connectedto the screen grid of the pentode amplier 38 while the collectorelectrode of the phototube 11 is connected to a fixed source ofpotential, namely, the resistance Voltage divider 31-34. Upon theoccurrence of a large signal on the input of the amplifier 38, theautomatic gain control signal developed by rectifier 113 and fed backthrough conductor 116, causes the control grid bias of amplifier 38 tobecome more negative by a relatively few volts. This action in turncauses the screen voltage of tube 38 to rise by a matter of 30 or 40volts. Because the emitter electrode of the phototube 11 is connected tothe screen grid it likewise rises in potential an equal amount, therebyreducing the phototube sensitivity, and hence the value of the inputsignal. Consequently,` it can be appreciated that the automatic gaincontrol circuit provided by the present invention is double acting inthe sense that it reduces both the signal amplitude as well as the gainof the tirst stage amplifier of the circuit to provide proper outputvoltage without undesirable distortion.

The applied input signal stabilized in the above-described manner, isfed through the wave shaping circuit comprising differentiator 45, 46and the parallel conductive path composed of capacitor 48 and resistor49 to produce a composite output signal such as shown in Fig. 3C of thedrawing. This composite differentiated signal with the reinserted baseportion is then supplied through the coupling conductor 54 and amplifier58 to the control grid of rst triode section 64 of multivibrator 64, 65where it serves to control the action of the multivibrator, and causesthe Same to produce an output square wave signal having a pulse widthproportional to the width of the object being gaged in the previouslydescribed manner. The outputs of both channels 24 and 25 of the steelmill width gage are then combined in the totalizing resistor 93 andV fedthrough integrating lter networks 89 to the differential amplier 97where the Si combined signals are compared with the referencepotential'picked off voltage divider 98 to provide an indication ofV anydeviation in width of the object being gaged from a' predeterminedstandard.

From the foregoing description, it can be appreciated that the inventionprovides a new and improved noncontacting widthgage which incorporatesas apart thereof a novel wave shaping input circuit arrangement for amultivibrator which overcomes the effects of edge cooling with regard tothe operation of the multivibrator, and docs not produce false responsesthereof due to the appearance of scale onr the object being gaged. Inaddition, theA invention provides a great-ly improved phototube gaincontrol' circuit which allows the non-contacting width gage to be usedwith objects having a wide range of luminosities.

ln a preferred embodiment of applicants novel width gage circuit, theparameters of the circuit had the below listed values'. It should beespecially noted that the values cited are for examples only, and thatthe invention is not to be construed as limited to the parameterslisted.

Resistors Resistor 31 megohms-- 8.2 Resistor 32 d0 2.2 Resistor 33 do2.2 Resistor 34 d0 2.2 Resistor 35 do 1.5 Resistor 40 do .1 Resistor 41ohms 470 Resistor 42 megohms-- 27 Resistor 43 do 15 Resistor 46 do .1Resistor 49 d0 10 Resistor 51 ohms 2200 Resistor 52 megohms .27 Resistor53 kiloohms 39 Resistor 56 megohms .1 Resistor 57 do .47 Resistor 59 do.1 Resistor 61 ohms 470 Resistor 62 megnhms 22 Resistor 67 do l5Resistor 68 do 1.0 Resistor 69 do 1.() Resistor 70 kiloohms 47 Resistor71 megohms 47 Resistor 72 do 47 Resistor 73 do .12 Resistor 74 kiloohms53 Resistor 75 do 10 Resistor 76 megohms 1 Resistor 77 kiloohms 150Resistor 86 megohms 4.7 Resistor 87 do 4.7 Resistor 88 do 1.8 Resistor91 do 1.5 Resistor 92v do 1.5 Resistor 93 klonhms 680 Resistor 98 do14.4 Resistor 99 do 15 Resistor 101 nhms 15 Resistor 102 kiloohms 11Resistor 103 ohms 5800 Resistor 104 do 8600 Resistor 106 megohms 1.0Resistor 108 nhms 4700 Resistor 109 do 6800 Resistor 112 megohms .1Resistor 114 do 1.0 Resistor 117 do 3.3 Resistor 118 do 22 Resistor 119110---- 10 Obviously, other modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that changes may be made herein which arewithin the full intended scope of the invention as defined by theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A non-contacting Width gage including in combination a pair ofphotoelectric devices positioned to view respective opposite edges of anobject being gaged, means for scanning the view of each of saidphotoelectric devices in the direction of the width of said object tothereby produce substantially square wave shape alternating electricsignals which are representative of the width of the object in the areaof view of the respective photoelectric device, a irst conductive pathincluding a pair of photoelectric device gain-control circuits eachincluding an electron discharge device having a plurality of controlelectrodes, each of said photoelectric devices being coupled between twocontrol electrodes of its respective electron discharge device, meansoperatively coupled to one of the two control electrodes of each of saidelectron discharge devices to which the associated photoelectric deviceis coupled for providing varying control electric signals thereto tothereby control the sensitivity of the respective photoelectric device,respective waveshaping circuits coupled to the output of each of saidelectron discharge devices, each of said wave-shaping circuits includinga bi-Stable multivibrator, a differentiating circuit coupled between theoutput of the electron discharge device and its respectivemultivibrator, and a second conductive path coupled between the outputof the electron discharge device and the input to the multivibrator inparallel circuit relationship with the differentiating circuit, and acommon output indicating circuit operatively coupled to the output ofboth of said bistable multivibrators.

2. A non-contacting width gage including in combination a pair ofphotoelectric devices positioned to view respective opposite edges of anobject being gaged, means for scanning the View of each of saidphotosensitive devices in the direction of the width of said object tothereby produce substantially square wave shape alternating electricsignals which are representative of the width of the object in the areaof view of the respective photoelectric device, a first conductive pathincluding a pair of photoelectric device gain-control circuits eachincluding an electron discharge device having at least control grid andscreen grid electrodes, each of said photoelectric devices being coupledbetween the control grid and screen grid electrodes of its respectiveelectron discharge device, means operatively coupled to the control gridelectrode of said electronl discharge device for providing varyingcontrol electric signals thereto, respective wave-shaping circuitsoperatively coupled to the output of each of said electron dischargedevices, each of said wave-shaping circuits including a bi-stablemultivibrator, a differentiating circuit coupled between the output ofthe electron discharge device and its respective multivi brator, and asecond conductive path coupled between the output of the electrondischarge device and the input to the multivibrator in parallel circuitrelationship with the differentiating circuit, and a common outputindicating circuit operatively coupled to the output of both of saidbi-stable multivibrators.

3. A non-contacting Width gage including in combina-` tion a pair ofphotoelectric devices positioned to view respective opposite edges of anobject being gaged, means for scanning the view of each of saidphotoelectric devices in the direction of the width of said object tothereby produce substantially square wave shape alternating electricsignals which are representative of the Width of the object in the areaof view of the respective photoelectric device, a first conductive pathincluding a pair of photoelectric device gain control circuits eachincluding an electron discharge device having at least control grid andscreen grid electrodes, each of said photoelectric devices being coupledbetween the control grid and screen grid electrodes of its respectiveelectron discharge device, a pair of rectifier networks each having theinput thereof operatively coupled to the output of its respectiveelectron discharge device and having the output thereof connected to thecontrol grid of said electron discharge device through a long timeconstant circuit, respective wave-shaping circuits coupled to the outputof each of said electron discharge devices, cach of said wave-shapingcircuits including a bi-stable multivibrator, a differentiating circuitcoupled between the output of the electron discharge device and itsrespective multivibrator, and a second conductive path including anattenuating impedance coupled between the output of the electrondischarge device and the input to the multivibrator in parallel circuitrelationship with the differentiating circuit, and a cornmon outputindicating circuit operatively coupled to the output of both of saidbi-stable multivibrators.

4. A non-contacting width gage including in combination a pair ofphotoelectric devices positioned to view respective opposite edges of anobject being gaged, means for scanning the view of each of saidphotoelectric devices in the direction of the width of said object tothereby produce substantially square Wave shape alternating electricsignals in the output of each of the photoelectric devices which arerepresentative of the width of the object in the area of view of therespective photoelectric device, a first conductive path includingrespective bi-stable multivibrators operatively coupled to the output ofeach of said photoelectric devices, wave shaping circuits coupledbetween the output of each of said photoelectric devices and therespective multivibrators thereof, each of said wave shaping circuitsincluding a differentiating circuit coupled between the output of thephotoelectric device and its respective multivibrator, and a secondconductive path coupled between the output of the photoelectric deviceand the input to the multivibrator in parallel circuit relationship withthe differentiating circuit, and a common output indicating circuitoperatively coupled to the output of both of said bi-stablemultivibrators.

5. A non-contacting width gage including in combination a pair ofphotoelectric devices positioned to view respective opposite edges of anobject being gaged, means for scanning the view of each of saidphotoelectric devices in the direction of the width of said object to 11thereby produce substantially squarewave shape alterna-ting electricsignals in thel output of each of theA photo-- electric devices whicharerepresentativeY of the width of the object in the area of View of therespective photoelectric device, a rst conductive path includingrespective bi-stable multivibrators operatively coupled to the output ofeach of said photoelectric devices, Wave shaping circuits coupledAbetween the output of each of said photoelectric devices and therespective multivibrators thereof, each of saidL Wave shaping circuitsincluding a diierentia'ting circuit coupled between the output of thephotoelectric device and its respective multivibrator for applying asignal to the multivibratio-n for triggering the same from one stablestate of operation to the other, and a second conductive path includingan attenuating irnpedance coupled between the output of thephotoelectric device and the input to the multivibrator in parallelcircuit relationship with the diierentiating circuit reinsert- 12 ing aportion of the original; signal into the dierentiated signall suppliedto the input of the multivibrator, and a common output indicati-ngcircuit operatively coupled to the output of both ofsaidbi-stablemulti-vibrators.

References Cited in the le of this patent UNITED STATES PATENTS2,035,907 McMaster et al Mar. 31, 1936 2,237,811 Cockrell Apr. 8, 19412,474,906 Meloon `uly 5, 1949 2,484,299 Labrum Oct. 11, 1949 2,548,590Cook Apr. 10, 1951 2,609,499 Gilson Sept. 2, 1952 2,617,932 CoughlinNov. 11, 1952 2,653,237 Johnstone et al Sept. 22, 1953 2,659,823Vossberg Nov. 17, 1953 2,674,915 Anderson Apr. 13, 1954

